Add assert_approx_eq

help/comparisons/assert_approx_eq/README.md

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+index.md

help/comparisons/assert_approx_eq/index.md

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+# Comparisons: assert_approx_eq
+
+https://crates.io/crates/assert_approx_eq
+
+The `assert_approx_eq` crate provides the `assert_approx_eq` macro. The `assertables` crate has a deliberately-similar macro because we want to make it easy to migrate.
+
+Both crates have the same syntax for a comparison that uses the default delta:
+
+```rust
+assert_approx_eq!(a, b); // default delta is 1.0e-6
+```
+
+The `assert_approx_eq` crate uses an optional delta such as:
+
+```rust
+assert_approx_eq!(a, b, 1); // delta is 1
+```
+
+The `assertables` crate uses an explicit macro name with a delta:
+
+```rust
+assert_in_delta!(a, b, 1); // delta is 1
+```
+
+We prefer the explicit macro name, rather than a form with an optional delta